Use of diverting agents for injection well stimulation

ABSTRACT

The injectivity profile of an injection well in fluid communication with an oil-bearing, heterogeneous formation, is improved by incorporating a diverting agent into the front portion of a micellar solution or by intermittently injecting micellar solution followed by a diverting agent-the result is to stimulate the reservoir rock and to obtain a uniform injectivity profile. The total amount of micellar solution useful to stimulate the injection well is 1-500 gallons per vertical foot of oil-bearing formation. The amount of diverting agent necessary will depend upon the heterogeneity of the formation; where intermittent slugs of micellar dispersion and diverting agent are injected, the amount of diverting agent can be from about 0.1 to about 50 or more volumes per volume of injected micellar dispersion. Examples of diverting agents include aqueous and hydrocarbon solutions containing fibrous material, laminated material, glutinous material, or other like materials which tend to &#39;&#39;&#39;&#39;block&#39;&#39;&#39;&#39; the reservoir rock. Preferably, the diverting agent is one that is soluble in water. A third slug can be injected to solubilize the diverting agent and optionally acid can be injected after the micellar solution and diverting agent to increase the injectivity index.

States nite atent Svaldi [54] USE OF DIVERTING AGENTS FOR INJECTION WELLSTIMULATION [72] Inventor: Marvin A. Svaldi, Morrison, C010.

[73] Assignee: Marathon Oil Company, Findlay,

Ohio

[22] Filed: July 13, 1971 [211 Appl. No.: 162,288

[52] US. Cl. ..l66/305 R, 166/274 [51] int. Cl. ..E21b 43/25 [58] Fieldof Search..l66/305 R, 274, 275, 284, 281, 166/282 [56] References CitedUNITED STATES PATENTS 3,336,977 8/1967 Amott ..l66/274 3,455,393 7/1969Bradley ..166/305 R 3,460,622 8/1969 Davis, Jr ..l66/275 X 3,470,95810/1969 Kinney ..166I305 R 3,482,635 12/1969 Pasini ..166/305 R3,556,221 1/1971 l-laws et al. ..166/305 R 3,557,873 1/1971 Owens..l66/274 3,568,772 3/1971 Gogarty et al. ....166/274 X 3,638,729 2/1972Parkermm. ....166/275 X 3,648,774 3/1972 Kirk ..l66/305 R OTHERPUBLICATIONS Tosch et al., Emulsion Slugs of Improved Viscosity for OilRecovery, Marathon Oil C0. Technical Disclosure Bulletin, Vol. No. 111,March, 1966, page 5.

Primary Examiner-Stephen J. Novosad Attorney-Joseph C. Herring et al.

[57] ABSTRACT The injectivity profile of an injection wellin fluidcommunication with an oil-bearing, heterogeneous formation, is improvedby incorporating a diverting agent into the front portion of a micellarsolution or by intermittently injecting micellar solution followed by adiverting agent-the result is to stimulate the reservoir rock and toobtain a uniform injectivity profile. The total amount of micellarsolution useful to stimulate the injection well is l-500 gallons pervertical foot of oil-bearing formation. The amount of diverting agentnecessary will depend upon the heterogeneity of the formation; whereintermittent slugs of micellar dispersion and diverting agent areinjected, the amount of diverting agent can be from about 0.1 to about50 or more volumes per volume of injected micellar dispersion.- Examplesof diverting agents include aqueous and hydrocarbon solutions containingfibrous material, laminated material, glutinous material, or other likematerials which tend to block the reservoir rock. Preferably, thediverting agent is one that is soluble in water. A third slug can beinjected to solubilize the diverting agent and optionally acid can beinjected after the micellar solution and diverting agent to increase theinjectivity index.

9 Claims, No Drawings USE OF DIVERTING AGENTS. FOR INJECTION WELLSTIMULATION BACKGROUND OF THE INVENTION hydrocarbon, surfactant, andaqueous medium. The

diverting agent can be an aqueous or hydrocarbon mixture containing asolubilized or suspended material which will effectively block the morepermeable zones within the heterogeneous formation.

2. Description of the Prior Art.

U. S. Pat. No. 3,174,546 to Flickinger teaches use of diverting agentsto effect a more uniform acidizing process.

' U. S. Pat. No. 3,193,007 to Kiel et al teaches controlling injectivityprofiles by injecting a surfactant solution followed by a temporaryplugging agent (e.g.,

polyvinyl acrylarnide) and this in turn followed by more surfactantsolution, etc.

U. S. Pat. No. 3,353,604 to Gibson et al. teaches improved stimulationby first injecting an aldehyde polymer (this is a diverting agent whichis slowly soluble in water) followed by acidizing or treating fluidthus, permeable channels are temporarily plugged to effect a moreuniform stimulation of the formation.

U. S. Pat. No. 3,455,393 to Bradley teaches modifying water injectionprofiles-by injecting an aqueous solution containing a viscosityincreasing agent with incrementally increasing concentrations of theviscosity additive. U. S. Pat. No. 3,467,188 to Gogarty teachesstimulation of water injection wells with oil-external micellardispersions. U. S. Pat. No. 3,474,865 to vGogar'ty et al teachesstimulation of water injection wells with water-extemal micellardispersions. These stimulation techniques are especially useful toincrease SUMMARY OF THE INVENTION Applicant has discovered a novelmethod of improving the injectivity profile of an injection well influid communication with a heterogeneous formation. This is accomplishedby injecting either an oil-extemal or a water-extemal micellardispersion containing a divertingagent in the front portion of themicellar dispersion or intermittently injecting a micellar dispersionand a diverting agent. The purpose of the diverting agent is to block orprevent subsequently injected micellar dispersion from substantiallyentering the higher permeable zone(s) of the reservoir, thus a moreuniform injectivity profile can be obtained. A' solvent to solubilizethe diverting agentcan be injected after the micellar dispersion andoptionally acid can be injected after or with the solvent to increasethe injectivity index of the injection well.

PREFERRED EMBODIMENTS OF THE INVENTION The micellar dispersions usefulwith this invention are comprised of hydrocarbon, surfactant, aqueousmedium, and optionally cosurfactant and/or electrolyte. Examples of suchmicellar dispersions are taught in U. S.-Pat. Nos. 3,254,714 to Gogartyet al.; 3,275,075 to Gogarty et al.; 3,497,006 to Jones et al.;3,506,070 and 3,506,071 to Jones. Examples of volume amounts includeabout 2 to about 90 percent hydrocarb'on,'about 5 to about 95 percentaqueous medium, at least about 4 percent surfactant, about-0.01 to about20 percent or more of cosurfactant, and about 0.001 to about 5 percentby weight of electrolyte. The hydrocarbon can be crude oil, a partiallyrefined fraction of crude oil (e.g., naphthas, gasoline, kerosene,etc.), a refined fraction of crude'oil (pentane, butane, decane, etc.)or a synthetic hydrocarbon (e.g., a halogenated hydrocarbon), etc. Thesurfactant is preferably a petroleum sulfonate having an averageequivalent weight of about 350 to about 525 and is preferably amono-valent cation containing sulfonate. The aqueous medium can berelatively soft water or brackish water, preferably the ions within thewater are compatible with the ions within the subterranean formation.The cosurfactant can be an aldehyde, alcohol, ether, ester,

' amine, or a like compound containing one or more like electrolyte canbe a water-soluble inorganic salt, inorganic base, or inorganic acid orthe organic equivalent thereof. Examples of specific components can befound in the above-enumerated patents. In addition, the micellardispersion can contain other additives to impart desired characteristicsin the formation, e.g., corrosion inhibitors, oxygen scavengers, etc.

The heterogeneous formations useful with this invention include thoseformations having two or more zones of substantially differingpermeabilities and/or differing fluid transmissibilities.Transmissibility is defined as the product of the effective permeability(to the flow of a particular fluid) and the vertical thickness of thepermeable zone divided by viscosity of the fluid. These differingpermeabilities and/or zonal fluid transmissibilities are generally dueto differences in single phase permeabilities and/or fluid saturations.Where a stimulation fluid is injected into such a formation, the fluidtends to enter the zone having the greatest transmissibility, thus thefluid is thieved and the lesser transmissive zones do not see the fluid.

From about 1 to about 500 gallons per vertical foot of oil-bearingformation of the micellar dispersion is normally sufficient to stimulatethe formation. Preferably about 20 to about 250 gallons per verticalfoot is useful. If sequential injection of the micellar dispersion andthe diverting agent is used, then each volume of the micellar dispersioncan be within the range of about 1 to about 500 gallons per verticalfoot of oil-bearing formation.

carrier The diverting agent can be incorporated into the micellardispersion or it can be a separate slug intermittently injected beforeand after the micellar dispersion. Examples of diverting agents includethose agents which will effectively reduce the mobility of an aqueous,hydrocarbon or micellar dispersion medium or which will effectivelyblock the reservoir rock (i.e., formation) from substantially receivingmicellar dispersion. Examples of such agents include partiallyhydrolyzed, high molecular weight acrylamides, polysaccharides,polyethylene oxides, carboxymethylcellulose, carboxyvinylpolymers, andlike materials. Also, the diverting agent can be a fibrous material,e.g., pliable, stringy, materials which tend to entangle or net in orover a crevice; granular material, e.g., a substantial rigid materialwhich tends to bridge against itself in a crevice without beingsubstantially distorted; and/or a laminated material, e.g., materialsformed of thin sheets or flakes, etc. The size of the diverting agentpreferably varies over a wide range so that an impermeable bridge ratherthan a filter is formed in the pores of the very permeable zones. Also,the diverting agent can be rock salt, wax such as flaked or granulatedbeeswax, camauba wax, microcrystalline hydrocarbon .wax, and othernatural and synthetic polymers. Also, fats and hardened oils, includinghydrogenated oils (e.g., animal oils, soybean oil, cottonseed oil, andlike oils) are useful. Especially useful are coal tar derivatives whichare preferably solid at substantially ambient temperature. In addition,synthetic diverting agents such as spherical balls, or sealer ballshaving a pliable veneer are especially useful in a cased well-the ballshave a sufficiently larger diameter than the perforations within thecased well and tend to plug the perforations.

The diverting agent is preferably dispersed in a carrier liquid or themicellar dispersion. The carrier liquid can be substantially aqueous orsubstantially hydrocarbon. Preferably it is aqueous since a hydrocarboncarrier liquid may increase the oil saturation in the immediate vicinityof the well bore and thus reduce the permeability of the formation tothe flow of water. Also, it is preferred that the carrier liquid becapable of suspending or keeping in suspension the diverting agent witha minimum of settling or separation. In addition, the carrier liquid ispreferably compatible with the formation fluids and the ions within thesubterranean forballs, neoprene, plastic, or like materials. The sealerballs substantially conform to the shape of the perforations and thusseal off that portion of the formation in communication through theperforation. The sealer balls are removed uphole or permitted to fallinto a basket at the terminable end of the casing before normaloperation of the injection well is resumed.

After the diverting agent is injected into the formation, a solvent tosolubilize the diverting agent can be injected to substantially removethe diverting agent from the immediate vicinity of the well bore. Forexample, sodium hypochlorite, hydrazine, or like material is usefulwherein the diverting agent is a partially hydrolyzed, highmolecularweight polyacrylamidethese particular solvents tend to removepolyacryl'amide that has become adsorbed onto the reservoir rock andthus increase the effective permeability of the formation to the flow ofinjection fluid. Of course, the particularsolvent to be injected shouldhave a capability of solubilizing the. previously injected divertingagent.

Thus, the particular diverting agent will dictate the parmation.Examples of carrier fluids include water,

hydrocarbon (e.g., crude oil, partially refined fractions of crude oil,etc.) and micellar dispersions. Where the liquid is substantiallyhydrocarbon, the preferred diverting agents include high molecularweight metallic soaps, polypropylene, polybutenes, and any compatiblehigh molecular weight polymer which tends to plug the formation.Examples of diverting agents preferred with aqueous carrier fluidsinclude partially hydrolyzed high molecular weight polyacrylamides,polysaccharides, carboxymethylcellulose, carboxyvinylpolymers,polyethylene oxides, like materials, and combinations thereof.

Where the well is cased, i.e., perforations are present in the casing topermit fluid communication with the formation, the diverting agent canbe sealer balls."

ticular solvent to be injected.

Also, an acidic solution can be injected after the micellar dispersionto further increasethe injectivity index of the injection well. Examplesof useful acids include aqueous solutions of hydrochloric and. sulfuricacids. The acids can have other additives incorporated therein to impartdesired characteristics; these additives are known in the art. Also, theparticular chosen acid is preferably compatible with the reservoir rock.

The diverting agent can be incorporated within the micellar dispersion.The'amount of diverting agent will be directly dependent upon the degreeof heterogeneity in the formation. For example, where the formation iscomposed of a lesser and a higher permeability zones, then only one"slug of diverting agent is necessary to block the higher permeabilityzone. However, where there are more than two substantially differingpermeabilities within the formation, then more than two separate slugsof diverting agents are desired. For example, an initial slug ofmicellar dispersion can be injected followed by a slug of divertingagent and then followed by another slug of micellar dispersion and this,in turn, followed by a slug of diverting agent; such can be repeateduntil the desired injectivity profile is obtained. Of course, the numberof differing permeabilities will dictate the number of diverting agentslugs to be injected. Where the diverting agent is to be suspended inthe micellar dispersion, then the diverting agent can be intermittentlyinjected while the micellar dispersion is injected. For example, to100,000 ppm of a partially hydrolyzed polyacrylamide can beintermittently mixed with an oil-external micellar dispersion andinjected as taught herein.

vwhen acid is injected after the micellar dispersion and the divertingagent, examples of volume amounts include 1 to about 500 gallons,preferably 20 to about 250 gallons of acid per vertical foot ofoil-bearing formation. Where the micellar dispersion is used to suspendthe diverting agent, it may be desirable to inject a slug of waterbetween the micellar dispersion and the acid slug; examples of volumeamounts of water include from about 0.1 to about 50 volumes of water pervolume of injected micellar dispersion. The water is desired to insulatethe micellar dispersion from the subsequently injected acid.

After the micellar dispersion and diverting agent is injected, water canbe injected into the injection well and normal operation resumed.Increased injectivity indexes are then realized. It may be desired totreat the injection well by this process at designated intervals, e.g.,every two months; however, such a treatment will depend upon theparticular reservoir and the desired injectivity indexes.

The following examples are presented to teach specific workingembodiments of the invention. Unless otherwise specified, all percentsare based on volume.

EXAMPLE I An injection wellin fluid communication with a heterogeneousformation 50 feet thick and having three substantially differingperrneabilities is treated by injecting a total of 12,500 gallons of anoil-external micellar dispersion comprised of 70 percent aqueous medium,percent ammonium petroleum sulfonate, 19 percent of hydrocarbon(straight run gasoline) and about 1 percent of n-hexanol. First there issubjected 2,500 gallons of the micellar dispersion, then 1,000 gallonsof the micellar dispersion containing 1,000 ppm of Dow Pusher 700 (apartially hydrolyzed, high molecular weight polyacrylamide marketed byDow Chemical Co., Midland, Michigan) is injected. The pressure gauge ofthe injection well indicates a pressure increase, thus, the mostpermeable zone is blocked by the 1,000 gallon slug. Thereafter, 4,000gallons of the micellar dispersion are injected; this slug flows intothe second most permeable zone. Thereafter, 1,000 gallons of themicellar dispersion are injected containing 1,000 ppm of the Dow Pusher700 polymer. Again, a pressure increase is realized. Thereafter, theresidue of the micellar dispersion, i.e. 4,000 gallons, is injectedthrough the injection well. Water is then injected into the injectionwell. An improved injectivity profile is realized as compared to theoriginal injectivity profile, i.e., more effective stimulation isobtained.

EXAMPLE I] EXAMPLE I" An injectivity well having a perforated casingwithin the well bore in fluid communication with a formation about 20feet thick is treated. The formation is characteristic of two differingtransmissibilities, that is, a lesser and a higher permeable zone. Thiswell is treated by first injecting 1,500 gallons of a micellardispersion defined in- Example I. Thereafter, there is injected 500gallons of the same micellar dispersion containing sealer balls, thenumber sufficient to seal 35 percent of the perforations within thecasing. Thereafter, 2,000 gallons of the micellar dispersion areinjected into the formation. Water is then injected. An improvedinjectivity profile is realized as compared to the original intivitrofile. lt is rio iintended that the invention be limited by thespecifics taught about. Rather, all equivalents obvious to those skilledin the art are intended to be equated within the scope of the inventionas defined within the specification and appended claims.

What is claimed is:

l. A process of improving the injectivity profile of an injection wellin fluid communication with an oil-bearing, heterogeneous formation, theheterogeneous formation having at least a lesser and a higher permeablezone(s), the process comprising injecting about 1 to about 500 gallonsof a micellar dispersion per vertical foot of the oil-bearing formationinto the formation and incorporating into the micellar dispersion orinto a carrier liquid a sufficient amount of a diverting agent tosubstantially block the more permeable zone(s) after a portion of themicellar dispersion enters the more permeable zone(s).

2. The process of claim 1 wherein a solvent to solubilize the divertingagent is injected after the micellar dispersion is injected into theformation.

3. The process of claim 1 wherein the diverting agent is a highmolecular weight organic polymer.

4. The process of claim 11 wherein the diverting agent is a partiallyhydrolyzed, high molecular weight polyacrylamide.

5. A process for improving the injectivity profile of an injection wellin fluid communication with an oilbearing, heterogeneous formationhavingsubstantially differing permeabilities, the process comprisinginjecting into the formation 1 to about 500 gallons of a micellardispersion per vertical foot of the formation, the micellar dispersionintermittently containing a high molecular weight organic polymer insufficient amounts to substantially block the more permeable zones ofthe formation, the result being to obtain a more uniform injectivityprofile.

6. The process of claim 5 wherein a solvent is injected after themicellar dispersion to substantially remove the organic polymer from theformation in the immediate vicinity of the injection well.

7. The process of claim 5 wherein the organic polymer is a partiallyhydrolyzed, high molecular 'weight polyacrylamide.

8. The process of claim 7 wherein sodium hypochlorite or hydrazine isinjected after the micellar dispersion to substantially remove any ofthe polyacrylamide that becomes adsorbed on the reservoir rock withinthe immediate vicinity of the well bore.

9. The process of claim 5 wherein an aqueous acidic solution is injectedafter the micellar solution to further increase the injectivity index.

2. The process of claim 1 wherein a solvent to solubilize the divertingagent is injected after the micellar dispersion is injected into theformation.
 3. The process of claim 1 wherein the diverting agent is ahigh molecular weight organic polymer.
 4. The process of claim 1 whereinthe diverting agent is a partially hydrolyzed, high molecular weightpolyacrylamide.
 5. A process for improving the injectivity profile of aninjection well in fluid communication with an oil-bearing, heterogeneousformation having substantially differing permeabilities, the processcomprising injecting into the formation 1 to about 500 gallons of amicellar dispersion per vertical foot of the formation, the micellardispersion intermittently containing a high molecular weight organicpolymer in sufficient amounts to substantially ''''block'''' the morepermeable zones of the formation, the result being to obtain a moreuniform injectivity profile.
 6. The process of claim 5 wherein a solventis injected after the micellar dispersion to substantially remove theorganic polymer from the formation in the immediate vicinity of theinjection well.
 7. The process of claim 5 wherein the organic polymer isa partially hydrolyzed, high molecular weight polyacrylamide.
 8. Theprocess of claim 7 wherein sodium hypochlorite or hydrazine is injectedafter the micellar dispersion to substantially remove any of thepolyacrylamide that becomes adsorbed on the reservoir rock within theimmediate vicinity of the well bore.
 9. The process of claim 5 whereinan aqueous acidic solution is injected after the micellar solution tofurther increase the injectivity index.